Cranial Nerves Flashcards
cranial nerves I and II exit
the only two that do not exit the brain at the level of the brainstem
cranial nerves III and IV exit
exit at the level of the midbrain
cranial nerves V, VI, VII, and VIII exit
exit at the level of the pons
cranial nerves IX, X, XI, and XII exit
exit at the level of the medulla
pure motor nerves
CN IV, VI, XI, and XII
eye movements and pupillary contriction
III, IV, VI
pure sensory nerves
I, II, VIII
mixed nerves
V, VII, IX, and X
parasympathetic fibers
III, VII, XI, and X
CN I Olfactory Nerve
sensory: responsible for the sense of smell
CN I Olfactory Nerve: path
nerve fibers traverse the skull through the cribriform plate where neurons synapse directly with the cortex with no relay through the thalamus
CN I Olfactory Nerve: pathology
head trauma can cause damage to the olfactory nerve as it travels through the cribriform plate leading to anosmia
olfactory groove meningiomas can also present with anosmia
CN II Optic Nerve
sensory: responsible fort visual sensory input
CN III Oculomotor Nerve
motor: innervates numerous extraocular muscles: superior rectus, inferior rectus, medial rectus, and inferior oblique as well as levator palpebrae
parasympathetic: pupillary constrictor and ciliary muscles (efferent limb of the pupillary reflex)
CN III Oculomotor Nerve: pathology
oculomotor nerve palsy can present with a combination of four possible clinical features: ptosis, ocular deviation, mydriasis, and diplopia
- ptosis secondary to loss of innervation of levator palpebrae muscle
- ocular deviation (down and out) and diplopia due to unopposed action of the lateral rectus and superior oblique muscles
- mydriasis occurs due to damage to the parasympathetic fibers which supply the pupillary constrictor and ciliary muscles
CN III Oculomotor Nerve: path etiologies
include trauma, diabetes, hypertension, subarachnoid hemorrhage, and compression from a posterior communicating aneurysm or uncal herniation
posterior communicating aneurysm
compresses the third nerve leading to ipsilateral pupillary dilatation and ophthalmoparesis
CN IV Trochlear Nerve
motor: innervates the superior oblique muscle, which is responsible for internal rotation and depression of the eye
CN IV Trochlear Nerve: pathology
exits the brainstem dorsally
of the cranial nerves, CN IV has the longest intracranial course
patients will complain of diplopia and difficulty descending stairs
on exam, patients will often tilt their head away from (contralateral to) the affected side to compensate for extorsion of the ipsilateral eye
CN V Trigeminal Nerve exits
at the level of the pons and trifurcates into three branches
- V1 Ophthalmic: traverses the skull through the Superior orbital fissure
- V2 Maxillary: traverses the skull through the foramen Rotundum
- V3 Mandibular: traverses the skull through the foramen Ovale
mnemonic: “Standing Room Only”
CN V Trigeminal Nerve
sensory: responsible for all modalities of sensation to the face
motor: innervates the muscles of mastication (masseter, temporalis, medial, and lateral pterygoids), tensor veli palati, anterior belly of the digastric, mylohyoid, and tensor tympani
- motor fibers exit via foramen ovale
CN V Trigeminal Nerve: Pathology
associated symptoms with a trigeminal lesion include impaired facial sensation and impaired hearing of the ipsilateral ear secondary to damage to the tensor tympani muscle
- can be seen in Wallenberg’s syndrome which is due damage to the lateral medulla from a posterior inferior cerebellar artery (PICA) ischemic stroke
trigeminal neuralgia
compression of the trigeminal nerve can lead to trigeminal neuralgia which presents with intermittent, severe sharp/stabbing-like paroxysms of the face, episodes usually occur for only a few seconds at a time
sensory exam normal
common triggers: brushing teeth, washing face, and strong winds
carbamazepine first line therapy
dura of anterior fossa
innervated by ophthalmic branch of trigeminal nerve (CN VI)
dura of posterior fossa
predominantly innervated by cervical roots C2 and C3 as well as CN X
CN VI Abducens Nerve
Motor: innervates lateral rectus muscle, which is responsible for lateral deviation (abduction) of the eye
CN VI Abducens Nerve: pathology
lesion to the abducens nerve will lead to dysfunction of the lateral rectus muscle and the unopposed action of the left medial rectus muscle causing the affected eye to be turned nasally
can be secondary to increased ICP
CN VII Facial Nerve
motor: innervates the stapedius, buccinator, posterior belly of the digastric, and muscles of facial expression including frontalis, corrugator, orbicularis oculi and oris, nasalis, mentalis, and platysma
sensory: responsible for lacrimation, salivation (submandibular, sublingual), taste from the anterior 2/3rds tongue and sensation of the external ear
CN VII Facial Nerve: pathology
Bell’s palsy is a facial nerve mononeuropathy that presents with acute weakness of upper and lower facial muscles secondary to nonspecific viral infection
- most common cause of facial nerve paralysis
- second most common is HSV reactivation
- treatment: prednisone to reduce inflammation +/- valacyclovir for severe cases
infection related facial mononeuropathies often make a complete or near-complete recovery and rarely recur
non-infectious causes of facial mononeuropathy include sarcoidosis, diabetes, Sjogren’s syndrome, and amyloidosis
Ramsay Hunt syndrome
also called geniculate neuralgia or nervus intermedius neuralgia
paroxysms of severe pain deep in the ear and can present as hearing loss, bitter taste, tinnitus, and vertigo secondary to viral spread to the vestibulocochlear nerve
vesicular rash on external acoustic meatus and lateral tongue
ramsay hunt syndrome pathophysiology
herpes zoster virus lies latent in geniculate ganglia after initial infection and reactivation causes inflammation of the nerve within the narrow stylomastoid foramen -> damage to the nerve
can cause facial nerve mononeuropathy
more seen in immunocompromised patients
CN VII Facial Nerve: taste
rarely affected in facial nerve mononeuropathies because taste fibers do not traverse through the stylomastoid foramen
facial nerve lesions proximal to the chorda tympani, which are uncommon, could present with a taste deficit on the ipsilateral side
CN VII Facial Nerve: hyperacusis
caused by weakness of the stapedius muscle because bone is unable to cover the oval window to protect it from low vibratory tones
Lyme disease
can cause unilateral or bilateral facial nerve palsies as well as multiple cranial neuropathies
CN VIII Vestibulocochlear Nerve exits
via the internal acoustic meatus
CN VIII Vestibulocochlear Nerve
sensory: responsible for auditory sensory input (cochlear nerve) and maintaining equilibrium (vestibular nerve)
Auditory Pathway
Spiral ganglion -> Superior olivary nucleus and trapezoid body -> Lateral lemniscus -> Inferior colliculus -> Medial geniculate nucleus -> auditory cortex
internal acoustic meatus is SSLIM
CN VIII Vestibulocochlear Nerve: pathology
BPPV: otoliths -> nausea and positional vertigo
Dx: Dix Hallpike. Tx Epley maneuver
brainstem auditory evoked potentials (BAEPs)
cochlear nerve represents wave I
if wave I is present without any other waveforms on BAEPs then this is concerning for brain death
unilateral peripheral vestibular dysfunction
patient falling towards the affected ear
CN IX Glossopharyngeal Nerve
motor: innervates stylopharyngeus
sensory: responsible for taste of posterior 1/3 tongue, salivation (parotid), and autonomic monitoring via chemo- and baroreceptors of the carotid body and sinus
baroreceptor reflex
essential in regulating responses to blood pressure changes through changes in sympathetic tone. when blood pressure drops, baroreceptors cause an increase in sympathetic drive to increase heart rate in an attempt to preserve perfusion to the brain.
central locations in the aortic arch and carotid sinus
- aortic arch baroreceptor information travels to the nucleus tractus solitarius, and then to the ventrolateral medulla, via the aortic nerve (Nerve of Cyon), which combines with the vagus nerve (CN X)
- carotid sinus baroreceptor information primarily reaches these same nuclei via the glossopharyngeal nerve (CN XI)
CN IX Glossopharyngeal Nerve: pathology
glossopharyngeal neuralgia
- presents with intense and paroxysmal pain of the ear and tonsillar fossa which can be triggered by coughing or swallowing
- syncope can occur due to inappropriate carotid sinus/body sensory fiber activation
most commonly asked cranial nerve-muscle innervation associations:
CN IV: superior oblique
CN VI: lateral rectus
CN V: anterior belly of the digastric and tensor tympani
CN VII: posterior belly of the digastric and stapedius
CN IX: stylopharyngeus
CN X Vagus Nerve
motor: innervates the muscles of the pharynx and larynx, and only one tongue muscle: palatoglossus
sensory: responsible for taste sensation of the epiglottis as well as visceral sensation of the heart, lungs, and GI tract
CN X Vagus Nerve: path
derives fibers from the nucleus ambiguus, the dorsal motor nucleus, and the nucleus solitarius
nucleus ambiguus -> branchial motor fibers that travel to the muscles of the pharynx and larynx
dorsal motor nucleus -> parasympathetic innervation to the heart, lungs, and GI tract
nucleus solitarius -> taste and visceral sensory information from the heart, lungs, and GI tract
CN X Vagus Nerve: pathology
recurrent laryngeal nerve is a pure motor branch of the vagus nerve which innervates the laryngeal muscles.
- damage to this nerve by trauma, thyroid surgery, or compression neoplasm can lead to hoarseness, dysphagia, and hypophonia
CN XI Spinal Accessory Nerve
motor: sternocleidomastoid and trapezius
CN XII Hypoglossal Nerve
motor: innervates the extrinsic muscles of the tongue (glenioglossus, hypoglossus, and styloglossus)
CN XII Hypoglossal Nerve pathology
lesion will lead to tongue deviation toward the pathologic side
Cavernous sinus includes
several cranial nerves: CN III, IV, VI, V1 and 2, and sympathetic nerve fibers
internal carotid artery
surrounds pituitary gland
Cavernous sinus pathology
CN VI is the closest to the ICA and is most likely to be damaged in carotid dissection
Cavernous Sinus Syndrome
presents with papilledema, proptosis, and painful ophthalmoplegia
- proptosis secondary to occlusion of ophthalmic veins
common cause is cavernous sinus thrombosis often secondary to infection from orbital cellulitis or sinusitis
diabetes is risk factor
cribriform plate
olfactory nerve
optic canal
optic nerve
superior orbital fissure
oculomotor, trochlear, abducens, ophthalmic branch of trigeminal
foramen rotundum
maxillary branch of trigeminal
foramen ovale
mandibular branch of trigeminal
internal auditory meatus
facial nerve and vestibulocochlear nerve
jugular foramen
glossopharyngeal, vagus, and spinal accessory
hypoglossal canal
hypoglossal nerve
foramen magnum
ascending fibers of spinal accessory nerve enter before exiting the jugular foramen
also contains medulla and vertebral arteries
foramen lacerum
contains greater petrosal and deep petrosal nerves
internal carotid artery runs along, but not technically through, this foramen
foramen spinosum
middle meningeal artery/vein and meningeal branch V3
corneal reflex
protective blink response
afferent limb: ophthalmic division of trigeminal nerve
efferent limb: facial nerve (VII) which innervates orbicularis oculi
pupillary reflex
constriction of both eyes in response to light
afferent limb: optic nerve -> pretectal nucleus -> bilateral Edinger Westphal nuclei
efferent limb: oculomotor nerve
- Edinger-Westphal nuclei -> preganglionic parasympathetic fibers to cilliary ganglia via oculomotor neuron -> postanglionic parasympathetic fibers to sphincter muscle of the iris and ciliary muscles
both ipsilateral and contralateral pupillary constriction can give insight into the integrity of the oculomotor nerves
pupillary reflex pathology
any lesion to the optic nerve can cause loss of both direct and consensual response
lesion to the ipsilateral oculomotor nerve and/or Edinger-Westphal nucleus leads to loss of direct pupillary reflex
lesion to the contralateral oculomotor nerve and/or Edinger-Westphal nucleus leads to loss of consensual pupillary reflex
baroreceptor reflex
helps regulate blood pressure by detecting changes via a baroreceptor located in the carotid sinus and aortic arch. Increased pressures marked by these receptors produce slower heart rates and drops in blood pressure. A decrease in blood pressure produces an increase in sympathetic tone and a decrease in parasympathetic tone.
afferent limb is the glossopharyngeal nerve for the carotid sinus and the vagus nerve for the aortic arch.
efferent limb is the vagus nerve (CN X).
gag reflex
afferent limb: glossopharyngeal nerve
efferent limb: vagus nerve
nucleus tractus solitarius
both taste (rostral nucleus) and baroreceptor (caudal nucleus) information
CN VII: taste to anterior 2/3 tongue
CN IX: taste to posterior 1/3 tongue and baroreceptor from carotid sinus
CN X: taste to the pharynx and baroreceptor from aortic arch
information travels to the VPM of the thalamus
nucleus ambiguus
corticobulbar input is bilateral
motor fibers to pharynx/larynx/palate via CN IX, X, and XI
superior salivatory nucleus
parasympathetic supply to oral and nasal cavity lacrimal and mucosal glands, via CN VII
inferior salivatory nucleus
parasympathetic supply to the parotid gland, via CN IX
remember that although CN VII runs through the parotid gland physically, the gland’s parasympathetic innervation comes from CN IX
